EP0419965A2 - Polyisocyanates for lacquers, a process for their preparation and their use - Google Patents

Abstract

Polyisocyanates for lacquers, characterised by the simultaneous presence of from 0.5 to 15 % by weight of triazine units, of from 5 to 20 % by weight of isocyanate groups in blocked form and of from 0 to 30 % by weight of other chemically incorporated urethane groups different from the blocked isocyanate groups, a process for preparing these lacquer polyisocyanates by reacting a) organic diisocyanates with b) blocking agents for isocyanate groups, c) amino-containing triazines and optionally d) organic polyhydroxy compounds of molecular weight 62 to 3,000, and the use of the lacquer polyisocyanates combined with organic polyhydroxy compounds as stoving enamel or for preparing a stoving enamel.

Description

The present invention relates to new paint polyisocyanates with blocked isocyanate groups, which among other things. are characterized by the presence of 1,3,5-triazine structural elements incorporated via urea groups, a process for the preparation of these lacquer polyisocyanates and their use in combination with organic hydroxyl compounds as stoving lacquer or for the production of a stoving lacquer.

The use of 1,3,5-triazine derivatives, in particular melamine, as a starting material for the production of paint binders has long been known:

N-methylolmelamine resins and corresponding alkoxylated compounds are known as crosslinkers for paints; see for example: T. Yamamoto, T. Nakamichi and O. Ohe in J. of Coat. Technology 60 , 51 (1988) or H. Dürr and M Schön in Kunstharznachrichten 45 , 17 (1986).

The use of melamine as a component in polyurethane resins or polyurethane coating compositions is also already known. DE-OS 2 737 402 describes isocyanate group-containing addition products of melamine and aromatic diisocyanates as buildable fillers

In contrast, EP-A-56 153 describes epoxy group-containing compounds of melamine-containing triisocyanates and glycid as fillers which can be incorporated in polyurethane resins and which have lower melting points and improved compatibility.

In accordance with DE-OS 2 938 309, isocyanate prepolymers are reacted with free melamine, which is used in the form of a polyester / melamine paste, to produce thermosetting coatings for glass bottles with particularly good adhesion.

DE-OS 3 609 687 describes thermosetting resins from e.g. Diphenylmethane diisocyanate and melamine are described. With carbodiimidization of the isocyanate, polycarbodiimide / melamine mixtures are produced as foam or powder, which cure at 230 ° C. to form heat and flame-resistant resins.

Reaction products from diisocyanates and melamine in the equivalent ratio NCO / NH₂ = 1: 1 are used, for example, in accordance with DE-OS 2 844 132 as a component for flame-retardant coating compositions or in accordance with Japanese application JP 59 041-320 (Derwent 84-096 976) as heat-resistant resins used.

Blocked polyisocyanates are also known. They are widely used in polyurethane chemistry for the production of polyurethane coatings. ZW Wicks in Progress of Organic Coatings 3 , 73 - 99 (1975) and 9 , 3 - 28 (1981) gives a summary of the chemistry of blocked isocyanates.

1,3,5-triazine group-containing polyisocyanates are high-melting compounds which are sparingly soluble in conventional organic solvents, cf. DE-OS 2 737 402, page 7, lines 23-25, page 8, lines 15-19; EP-A-56 153, page 1, lines 12-15, page 7, lines 24-27 and DE-OS 3 609 687, page 15, lines 18-20.

Although the incorporation of 1,3,5-triazine structural elements often imparts desirable advantageous properties to polyurethane plastics, and although, as the abovementioned prior art shows, there has been no lack of attempts to obtain the advantageous properties of 1,3,5-triazine To use structural units in polyurethanes, 1,3,5-triazine group-containing polyisocyanates have hitherto hardly been used in practice because of their high melting point and their poor solubility in organic solvents. In particular, as coating raw materials, products that are free of turbidity are required in common physiologically harmless solvents.

It was therefore the object of the invention to provide 1,3,5-triazine structural elements containing polyisocyanates, which mentioned Do not have disadvantages that have a low melting point and are soluble in common paint solvents. They should be easy to prepare and implement as a solution or soluble solid resin with compounds that are reactive towards isocyanate groups, in particular polyhydroxyl compounds, to give high-quality polyurethane plastics, in particular lacquer layers.

This object was achieved by providing the lacquer polyisocyanates with blocked isocyanate groups described in more detail below. In the context of the invention, "lacquer polyisocyanates" include both polyisocyanates, i.e. to understand certain individual compounds as well as mixtures of polyisocyanates with blocked isocyanate groups, as are obtained when carrying out the process according to the invention.

The invention was based on the surprising observation that blocked polyisocyanates containing 1,3,5-triazine structural elements, in contrast to the corresponding unblocked polyisocyanates, have a comparatively low melting point and good solubility in conventional paint solvents. This fundamental difference between the blocked isocyanates on the one hand and the unblocked polyisocyanates on the other hand was by no means obvious since it is generally not observed in the case of the usual polyisocyanates in polyurethane chemistry.

• (i) 0,5 - 15 Gew.-% an über Harnstoffgruppen ein­gebauten Struktureinheiten der Formel
  
• (ii) 5 - 20 Gew.-% an Isocyanatgruppen (berechnet als -NCO) in mit Blockierungsmitteln für Iso­cyanatgruppen blockierter Form und
• (iii) 0 - 30 Gew.-% an sonstigen, von den blockier­ten Isocyanatgruppen verschiedenen, chemisch eingebauten Urethangruppen der Formel
  -NH-CO-O- .

The invention relates to lacquer polyisocyanates with blocked isocyanate groups, characterized by the simultaneous presence of

• (i) 0.5-15% by weight of structural units of the formula incorporated via urea groups
  
• (ii) 5-20% by weight of isocyanate groups (calculated as -NCO) in a form blocked with blocking agents for isocyanate groups and
• (iii) 0-30% by weight of other chemically incorporated urethane groups of the formula which differ from the blocked isocyanate groups
  -NH-CO-O-.

• a) organische Diisocyanate des Molekulargewichtsbe­reichs 160 - 300 mit
• b) Blockierungsmitteln für Isocyanatgruppen,
• c) Aminogruppen aufweisenden Triazinen der Formel
  
  in welcher
  R für eine Aminogruppe oder einen gegenüber Iso­cyanatgruppen inerten Substituenten steht
  und gegebenenfalls
• d) organischen Polyhydroxylverbindungen des Moleku­largewichtsbereichs 62 - 3.000
  umsetzt, wobei die Menge des Blockierungsmittels b) in einer zur Blockierung von 20 - 90 % der Isocyanatgruppen der Komponente a) ausreichenden Menge und die Komponen­ten c) und d) in einer solchen Menge eingesetzt werden, die einem Äquivalentverhältnis von nach der Blockie­rungsreaktion noch vorliegenden freien Isocyanatgruppen zu Amino- und Hydroxylgruppen von 0,65 : 1 bis 1,05 : 1 entsprechen, wobei das Äquivalentverhältnis von Amino­gruppen der Komponente c) zu Hydroxylgruppen der Kompo­nente d) bei 1 : 0 bis 1 : 20 liegt, und wobei die Re­aktionpartner a) bis d) in beliebiger Reihenfolge mit­einander umgesetzt werden, wobei jedoch vorzugsweise die Komponente c) nicht vor den Komponenten b) und d) mit der Komponente a) zur Reaktion gebracht wird.

The invention also relates to a process for the preparation of these paint polyisocyanates, which is characterized in that

• a) organic diisocyanates with a molecular weight of 160-300
• b) blocking agents for isocyanate groups,
• c) amino groups-containing triazines of the formula
  
  in which
  R represents an amino group or a substituent which is inert towards isocyanate groups
  and if necessary
• d) organic polyhydroxyl compounds in the molecular weight range 62-3,000
  reacted, the amount of blocking agent b) being used in an amount sufficient to block 20-90% of the isocyanate groups of component a) and components c) and d) in an amount which is still present after the blocking reaction in an equivalent ratio correspond to free isocyanate groups to amino and hydroxyl groups from 0.65: 1 to 1.05: 1, the equivalent ratio of amino groups of component c) to hydroxyl groups of component d) being 1: 0 to 1:20, and the reactants a) to d) are reacted with one another in any order, but preferably component c) is not reacted with component a) before components b) and d).

The invention finally also relates to the use of the lacquer polyisocyanates in combination with organic polyhydroxyl compounds as stoving lacquer or for the production of a stove enamel for any heat-resistant substrates, especially for wire painting.

When carrying out the process according to the invention for the preparation of the new coating polyisocyanates with blocked isocyanate groups, simple starting diisocyanates a) are reacted with blocking agents b), 1,3,5-triazine derivatives c) and optionally organic polyhydroxyl compounds d) in the sense of an isocyanate addition reaction. "Blocked isocyanate groups" naturally arise here when reacting with the blocking agents b) which are monofunctional to isocyanate groups, while the term "urethane groups" used under (iii) only includes the urethane groups formed by reaction with polyhydroxyl groups d).

The amount of blocking agent b) is measured so that it is sufficient to block 20-90%, preferably 35-80% and particularly preferably 50-70% of the isocyanate groups of the starting diisocyanates a). The amount of components c) and d) is such that the equivalent ratio of the excess isocyanate groups of component a) to the amino and hydroxyl groups of components c) and d) compared to the blocking agents b) is 0.65: 1 to 1, 05: 1, preferably 0.8: 1 to 1.0: 1, the equivalent ratio of the amino groups of component c) to the hydroxyl groups of component d) being 1: 0 to 1:20, preferably 1: 0 to 1: 4 and particularly preferably 1: 0 to 1: 1.

Suitable starting diisocyanates a) are any aromatic, aliphatic or cycloaliphatic diisocyanates in the molecular weight range 160-300 such as 1,4-phenylene diisocyanate, 2,4- and 2,6-diisocyanatotoluene (TDI) and any mixtures of these isomers, diphenylene-2,4-methane '- and / or -4,4'-diisocyanate, 1,5-naphthylene diisocyanate, 2-methylpentane-1,5-diisocyanate, 1,5-hexane diisocyanate, 1,6-hexane diisocyanate (HDI), 1,3- and 1 , 4-cyclohexane diisocyanate and any mixtures of these isomers, 3,5,5-trimethyl-3-isocyanatomethyl-cyclohexane isocyanate (IPDI) and dicyclohexylmethane-2,4'- and / or -4,4'-diisocyanate and any mixtures of these diisocyanates.

Diisocyanates to be used with particular preference are 2,4-diisocyanatotoluene and 2,6-diisocyanatotoluene, the technical mixtures consisting of these isomers and 4,4′-diisocyanatodiphenylmethane and 2,4′-diisocyanatodiphenylmethane, mixtures consisting of these isomers or any mixtures of the here mentioned aromatic diisocyanates.

Suitable blocking agents b) are the monofunctional compounds customary for blocking isocyanate groups, as mentioned, for example, in ZW Wicks, Progress in Organic Coatings 3 , 73 ff (1975) and 9 , 3 ff (1981). Phenols, aliphatic alcohols, oximes and lactams are preferred. Examples of blocking agents b) which may be mentioned are: phenol, cresol, xylenol and their technical isomer mixtures, isopropanol, cyclohexanol, 1-methoxy-2-propanol (MP), diethylene glycol monoethyl ether, benzyl alcohol, butanone oxime, cyclohexanone oxime and ε-caprolactam, of which cresol, 1-methoxy-2-propanol, butanone oxime and ε-caprolactam are particularly preferred.

in welcher
R für einen gegenüber Isocyanatgruppen inerten orga­nischen Rest, vorzugsweise einen C₁-C₄-Alkyl-, Phenyl- oder einen C₁-C₆-Alkoxyrest oder, besonders bevorzugt, für eine Aminogruppe steht.Suitable 1,3,5-triazine derivatives c) are compounds of the formula

in which
R represents an organic radical which is inert towards isocyanate groups, preferably a C₁-C₄-alkyl, phenyl or a C₁-C₆-alkoxy radical or, particularly preferably, an amino group.

A particularly preferred 1,3,5-triazine derivative c) is melamine.

Possible polyhydroxyl compounds d) to be used are preferably diols and / or triols of the molecular weight range 62-350, but also a higher molecular weight polyhydroxyl compound having a molecular weight above 350 and up to 3,000.

Suitable polyhydroxyl compounds of the molecular weight range 62-350 are, for example, ethylene glycol, propanediols, butanediols, hexanediols, di-, tri- or tetraethylene glycol, di-, tri- or tetrapropylene glycol, neopentyl glycol, 2-ethyl-1,3-hexanediol, 2,2,4 -Trimethyl- 1,3-pentanediol, 1,4-bis (hydroxymethyl) cyclohexane, 2,2-bis (4-hydroxycyclohexyl) propane, trimethylolpropane, glycerol, hexanetriol, N, N ′, N˝-tris (2-hydroxyethyl) isocyanurate (THEIC) and pentaerythritol.

Higher molecular weight polyhydroxyl compounds, which are by no means preferred over the low molecular weight polyhydroxyl compounds mentioned by way of example, are, for example, the known polyhydroxy polyesters as obtained from dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid or adipic acid with excess polyols of the type mentioned above. As higher molecular weight polyols it is also possible, but also less preferred, to use polyhydroxy polyethers known per se, such as are obtainable by alkoxylation of low molecular weight starter molecules.

When carrying out the process according to the invention, it is of course also possible in each case to use mixtures of the starting materials mentioned.

When carrying out the process according to the invention, the starting materials b), c) and, if appropriate, d) are reacted in any order with the diisocyanate component a), with the only restriction that component c) preferably does not precede components b) and d) are used. This means that For example, a) can be implemented in one step with a mixture of b), c) and d) or else that a) first with b) or with d) or with a mixture of b) and d) and then with c) or can be reacted with mixtures of c) and b) or from c) and d).

The reactions mentioned are generally carried out within the temperature range from 20 to 200 ° C., preferably 60 to 180 ° C.

According to a preferred embodiment of the process according to the invention, the starting diisocyanate a) is blocked with the blocking agent b) in the stated ratio. Depending on the type of blocking agent, the blocking takes place in the temperature range from 20 to 200 ° C., preferably at 60 to 160 ° C., until the calculated NCO content is reached or slightly below. After the blocking has ended, the solvent is then added, provided that a dissolved end product is to be prepared, and in a second reaction step the reaction of the partially blocked diisocyanate with melamine c), which is optionally added in a mixture with polyol d) used, in the temperature range from 60 - 180 ° C, preferably 80-160 ° C, carried out. As a rule, the polyol d), which may also be used, initially reacts at approximately 80 ° C. and then melamine c) at an elevated reaction temperature, preferably at approximately 140 ° C. The implementation is finished when a clear solution has been created, or that solvent-free resin is clearly soluble in, for example, acetone, and the free isocyanate group content of the reaction mixture has dropped to a value of less than 0.5% by weight.

According to this preferred process variant, lacquer polyisocyanates according to the invention can be prepared as solutions in lacquer solvents or as solvent-free resins, which as a rule solidify from the melt as a solid resin.

According to a further embodiment of the process according to the invention, the blocking carried out as the first reaction step already takes place in the presence of a suitable solvent, which is followed by the reactions with the other reaction partners in accordance with the preferred embodiment just described.

A further embodiment of the process according to the invention can consist, for example, of a one-pot reaction in which diisocyanate a), blocking agent b), melamine c) and optionally polyol d) are heated together, the aliphatic polyol initially reacting in the range from 60 to 90 ° C. the preferred phenolic blocking agent is reacted in the range from 90 to 120 ° C. and the reaction with the melamine is finally carried out in the range from 120 to 140 ° C. The individual reaction stages overlap and can usually be followed using exothermic heat with a fading tone after complete conversion.

Only in exceptional cases and by no means preferred is it possible to first react the diisocyanate a) with the melamine c) and optionally the polyol d) until the calculated NCO content has been reached, and only then to block the remaining isocyanate groups with the blocking agent b). perform.

The process according to the invention is generally carried out in solution, but it depends on the properties of the desired end product, such as Degree of branching and melt viscosity, also possible to work in the melt.

Suitable solvents are all conventional paint solvents known per se which are inert to isocyanate groups, such as, for example, ethyl acetate, butyl acetate, ethylene glycol monomethyl or ethyl ether acetate, 1-methoxypropyl-2-acetate, 2-butanone, 4-methyl-2-pentanone, cyclohexanone , Toluene, xylene, solvent naphtha or mixtures thereof. Also usable as solvents, but less preferred are plasticizers such as those based on phosphoric acid, sulfonic acid or phthalic acid esters. In addition to the paint solvents that are inert to NCO groups, it is also possible to use solvents that are partially reactive towards NCO groups. These solvents are then added only after the reaction is almost complete, for example when the NCO content is ≦ 0.5%, which means that the lacquer polyisocyanates prepared essentially in the absence of such solvents are dissolved in such solvents after their preparation can. Suitable are preferably monofunctional, aliphatic, cycloaliphatic, araliphatic alcohols or also phenols such as isopropanol, n-butanol, n-octanol, 2-methoxyethanol, 2-ethoxyethanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, 1-methoxy-2-propanol; Cycloalkanols such as cyclopentanol or cyclohexanol; Aralkanols such as benzyl alcohol or phenols such as cresol or xylenol.

The fact that the monohydric alcohols or phenols mentioned here as solvents can also be used as blocking agents b) already shows that when such alcohols or phenols are used as solvents they are not included in the calculation of the quantitative ratios of the reactants a) to d ) come in, but are only used as solvents after the reaction according to the invention.

• 1. Niedermolekulare, mehrwertige Alkohole mit einem maximalen Molekulargewicht von 350 und einer bei 2 bis 4 liegenden Hydroxylfunktionalität wie sie schon oben als Polyole d) beispielhaft aufgeführt wurden sowie aber z.B. auch 2,2-Bis[4-(2-hydroxy­ethoxy)-phenyl]propan, 2,2-Bis[4-(2-hydroxyprop­oxy)-phenyl]propan, Maleinsäure-bis-ethylenglykol­ester oder Adipinsäure-bis-ethylenglykolester.
• 2. Höhermolekulare Polyhydroxylpolyester des Moleku­largewichtsbereichs 351 - 4.000, wie sie durch Um­setzung von mehrbasischen Carbonsäuren wie z.B. Adipinsäure, Phthalsäure, Tetrahydrophthalsäure, Hexahydrophthalsäure oder von deren Anhydriden mit überschüssigen Mengen an mehrwertigen Alkoholen der unter 1. beispielhaft genannten Art zugänglich sind.
• 3. Aliphatisch gebundene Hydroxylgruppen aufweisende Oligourethane des Molekulargewichtsbereichs 200 - 2.000, wie sie durch Umsetzung der bereits unter 1. genannten, gegebenenfalls Ethergruppen aufwei­senden Alkandiole oder -triole mit unterschüssigen Mengen an Diisocyanaten der auch als erfindungsge­mäße Ausgangsmaterialien geeigneten und oben unter a) genannten Art erhalten werden und wie sie bei­spielsweise in DE-PS 1 644 794 oder in GB-PS 1 195 886 beschrieben sind.
• 4. Hydroxylgruppenhaltige Copolymerisate, wie sie durch Copolymerisation von z.B. Hydroxyalkylacry­ laten bzw. -methacrylaten mit Acryl- bzw Meth­acrylsäurealkylestern, sowie gegebenenfalls wei­teren olefinisch ungesättigten Monomeren und/oder wie sie gemäß der DE-OS 2 137 239 aus Styrol-Ma­leinsäure-Copolymerisaten durch teilweise Vereste­rung der Säuregruppen mit Ethylenoxid erhalten werden.
• 5. Hydroxylgruppen-aufweisende Polycarbonate der an sich bekannten Art, wie sie z.B. durch Umsetzung von Diolen wie 1,3-Propandiol, 1,4-Butandiol und/­oder 1,6-Hexandiol, Di-, Tri- und/oder Tetraethy­lenglykol mit Diarylcarbonaten, z.B. Diphenyl­carbonat, oder Phosgen hergestellt werden können, vorzugsweise Polycarbonate auf Basis von 1,6-Hexan­diol sowie gegebenenfalls modifizierend wirkende Co-Diole in untergeordneten Mengen (ca. 5 - 35 Mol-% der Diole). Auch Polycarbonate auf Basis von HO(CH₂)₆-O-CO-(CH₂)₅-OH kommen in Frage.

The coating polyisocyanates according to the invention are valuable reactants for organic polyhydroxyl compounds and can be used in combination with such polyhydroxyl compounds as stoving enamels or for the production of stoving enamels for any heat-resistant substrates. Suitable polyhydroxyl compounds for the production of coatings of this type are, for example, the compounds mentioned below under 1 to 5 or any mixtures of such compounds:

• 1. Low molecular weight, polyhydric alcohols with a maximum molecular weight of 350 and a hydroxyl functionality of 2 to 4, as already exemplified above as polyols d), but also, for example, 2,2-bis [4- (2-hydroxyethoxy) phenyl ] propane, 2,2-bis [4- (2-hydroxypropoxy) phenyl] propane, maleic acid bis ethylene glycol ester or adipic acid bis ethylene glycol ester.
• 2. Higher molecular weight polyhydroxyl polyesters of the molecular weight range 351-4,000, as are obtainable by reacting polybasic carboxylic acids such as adipic acid, phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid or their anhydrides with excess amounts of polyhydric alcohols of the type mentioned in example 1.
• 3. Aliphatically bound hydroxyl group-containing oligourethanes of the molecular weight range 200-2,000, as obtained by reacting the alkane diols or triols mentioned under 1, optionally containing ether groups, with deficient amounts of diisocyanates of the type which are also suitable as starting materials according to the invention and are mentioned above under a) and how they are described for example in DE-PS 1 644 794 or in GB-PS 1 195 886.
• 4. Copolymers containing hydroxyl groups, such as those obtained by copolymerization of, for example, hydroxyalkylacry latates or methacrylates with acrylic or methacrylic acid alkyl esters, and optionally further olefinically unsaturated monomers and / or as obtained from styrene-maleic acid copolymers according to DE-OS 2 137 239 by partial esterification of the acid groups with ethylene oxide.
• 5. Hydroxyl group-containing polycarbonates of the type known per se, such as, for example, by reacting diols such as 1,3-propanediol, 1,4-butanediol and / or 1,6-hexanediol, di-, tri- and / or tetraethylene glycol Diaryl carbonates, for example diphenyl carbonate, or phosgene can be prepared, preferably polycarbonates based on 1,6-hexanediol and optionally modifying co-diols in minor amounts (approx. 5-35 mol% of the diols). Polycarbonates based on HO (CH₂) ₆-O-CO- (CH₂) ₅-OH are also suitable.

The compounds mentioned by way of example in 2 and 3 are the preferred reactants for the coating polyisocyanates according to the invention with blocked isocyanate groups in the production of stoving enamels. In addition to the reaction partners mentioned by way of example, there may also be other compounds which are reactive toward isocyanate groups in the stoving lacquers, although this is generally less preferred. In this context, for example, hydroxyl-containing oligomeric epoxides, imide esters, imide ester amides, Hydantoins or amino group-containing compounds such as hexamethylenediamine, melamine / formaldehyde resins or aminopolyethers.

By choosing the molecular weight of the polyhydroxyl compounds to be used, the macroscopic properties of the sheet formed in the use according to the invention can be varied in a simple manner. In general, the use of higher molecular weight polyhydroxyl compounds leads to more elastic coatings, the use of lower molecular weight polyhydroxyl compounds leads to harder coatings.

In the use according to the invention, the lacquer polyisocyanates according to the invention are combined with the polyhydroxyl compounds mentioned by way of example in such proportions that 0.1-10, preferably 0.2-2, particularly preferably 0.5-1.2, hydroxyl groups are present for each blocked isocyanate group of the lacquer polyisocyanates according to the invention the reactive component containing hydroxyl groups is eliminated.

The combinations of the lacquer polyisocyanates according to the invention with the polyhydroxyl compounds mentioned by way of example can be used as such as stoving lacquer. However, they can also be mixed with auxiliaries and additives such as solvents, catalysts, pigments and the like.

Suitable solvents are in particular the solvents already mentioned as examples above. In case of If monohydric alcohols or phenols are used as solvents, they are displaced by the non-volatile polyhydroxyl compounds during the baking process, so that they distill off from the reaction mixture together with the blocking agent during the baking process. For the wire coating preferred in accordance with the invention, 15 to 75, in particular 20 to 60% by weight solutions of the combinations of coating polyisocyanate and polyhydroxyl compounds are generally used.

Examples of catalysts to be used according to the invention are described in the plastics handbook (ed. Becker / Braun), vol. 7, polyurethanes, pp. 92 ff, Carl Hanser Verlag, Munich Vienna 1983. For example, the catalysts described in DE-AS 2 626 175, column 7, line 35 to column 8, line 27 are also suitable. Organic metal catalysts such as, in particular, organic titanium, zinc or tin compounds such as tetraisopropyl titanate, zinc octoate, dibutyltin oxide or dibutyltin dilaurate are particularly suitable.

The catalysts are used, if at all, in an amount of 0.01 to 5.0, preferably 0.1 to 3.0% by weight, based on the blocked polyisocyanates according to the invention.

The by mixing at room temperature from the above-mentioned essential components or auxiliaries and Mixtures obtained from additives are stable in storage at room temperature or moderately elevated temperature (up to approx. 50 ° C.) and react when heated to temperatures above 60 ° C., preferably from 100 to 500 ° C. and in particular from 180 to 400 ° C. with simultaneous evaporation of the any volatile constituents (eg solvents) present to form crosslinked plastics.

The stoving lacquers produced using the lacquer polyisocyanates according to the invention are suitable for lacquering any heat-resistant substrates, in particular glass fibers and particularly preferably metal wires. The stoving lacquers consisting of combinations of the lacquer polyisocyanates according to the invention with organic polyhydroxyl compounds or mixtures of such combinations with auxiliaries and additives of the type mentioned can be applied to the substrates by all methods of coating technology, which is followed by curing of the coating within the above-mentioned temperature ranges.

In the preferred wire coating, the wires are coated according to the known immersion, roller application or suction felt processes, followed by drying, ie curing of the coating layers in the usual drying ovens within the temperature ranges mentioned. When using the products according to the invention as crosslinkers for wire coatings Particularly noteworthy here are the excellent adhesion to the wire and the possible high painting speed in comparison to conventional known products of the prior art.

Because of the excellent electrical and mechanical properties of the plastics formed from the paint polyisocyanates according to the invention and the polyhydroxyl compounds mentioned by way of example under the action of heat, the combinations of paint polyisocyanates according to the invention and the polyhydroxyl compounds mentioned by way of example, or the mixtures of these combinations with the auxiliaries and additives mentioned by way of example, are also suitable for the production of insulating fabrics or for the impregnation of electric motors.

In the examples below, all percentages relate to percentages by weight. The blocked NCO group contents were calculated as "NCO", ie using a molecular weight of 42. The contents of urethane groups relate exclusively to the urethane groups formed by the reaction of isocyanate groups with polyhydric alcohols and therefore do not include the blocked isocyanate groups formed from isocyanate groups and monohydric alcoholic or phenolic blocking agents, which of course also chemically represent urethane groups.

Examples example 1 a) Manufacturing

To 2064 parts by weight of diisocyanatotoluene (2,4- and 2,6-isomers in a weight ratio of 8: 2), starting at 80 ° C, 1,537 parts by weight of cresol (technical isomer mixture) are added dropwise with heating to 130 ° C. over the course of about 1 hour. The _mixture is left to react for about 8 hours to 15 hours at _120-140 ° C. until an NCO content of 11.0% is reached (NCO _theor. = 11.1%). It is dissolved with cooling by adding 5,000 parts by weight of 1-methoxypropyl-2-acetate and a suspension of 399 parts by weight of melamine in 1,000 parts by weight of 1-methoxypropyl-2-acetate is added at 80 ° C. The mixture is quickly heated to 140 ° C. with vigorous stirring of the suspension. After a reaction time of about 3 hours, a clear solution is obtained; after 1 hour of stirring, the reaction is complete, the free NCO content is <0.1%.

A clear solution of the blocked isocyanate is obtained with the following characteristics (all the information here and in the following preparation examples relates to the Solution): Concentration: 40% Viscosity _η (23 ° C): 28,000 mPas free NCO content: <0.1% blocked NCO content: 5.9% (Analysis method: 30 min / 180 ° C with di-n-butylamine in o-dichlorobenzo) blocked NCO content (calc.): 6.0% 1,3,5-triazine units (calc.): 2.5% Urethane groups (calc.): 0%

b) Use

200 parts by weight of a polyester with an OH number of 395, made from 40.8% trimethylolpropane, 14.2% ethylene glycol and 45.0% phthalic anhydride, are refluxed in 800 parts by weight of the same parts by weight of cresol and xylene at temperatures up to 130 ° C solved. 1,000 parts by weight of the 40% solution of the blocked polyisocyanate prepared as described under a) and 6 parts by weight of an aldimine based on butyraldehyde and aniline as catalyst are added to the solution obtained.

A copper wire 0.7 mm in diameter is coated with the solution prepared in this way. Painting furnace: vertical with felt scraper and 6 pull-throughs Oven length: 4 m Oven temperature: 350 ° C Increase in diameter due to painting: 40 - 50 µm Painting speed: 10 - 16 m / min

The enamelled wire thus obtained can be tinned within 9 seconds at 320 ° C. and has a pencil hardness of 4 H, which is unchanged even after immersion in ethanol heated to 60 ° C. for half an hour.

When using a conventional, commercially available coating system which differs only in terms of the nature of the hardener from the described coating system according to the invention [an equivalent amount of a blocked isocyanate, consisting of the reaction product of 55.6% diisocyanatotoluene (2,4- and 2- 6-isomers used in a weight ratio of 8: 2), 14.3% trimethylolpropane and 30.1% phenol], the enamelled wire obtained cannot be tinned at 320 ° C. at all or only after a considerably longer time than 9 seconds. The pencil hardness drops to HB after half an hour of ethanol treatment at 60 ° C.

Example 2 a) Manufacturing

A solution of 1,408 parts by weight of phenol in 3,000 parts by weight of 1-methoxypropyl-2-acetate is added dropwise to 2,172 parts by weight of diisocyanatotoluene (2,4- and 2,6-isomers in a weight ratio of 8: 2) at 120 ° C. in about 30 minutes. The _{mixture is left to} react at 120 ° C. for about 2 hours and, after reaching an NCO content of 6.7% (NCO _theor. = 6.4%), is allowed to cool. At 40 ° C. and an NCO content of the solution of now 6.3%, a suspension of 419 parts by weight of melamine in a further 3,000 parts by weight of 1-methoxypropyl-2-acetate is allowed to flow in. The mixture is heated to 140 ° C. with stirring. After about 1.5 hours, the mixture becomes clear and the reaction is ended after stirring at 140 ° C. for 1 hour.

A clear light yellow colored solution is obtained with the following characteristics: Concentration: 40% Viscosity _η (23 ° C): 3,240 mPas free NCO content: 0.4% blocked NCO content (found): 6.6% blocked NCO content (calc.): 6.3% 1,3,5-triazine units (calc.): 2.6% Urethane groups (calc.): 0%

b) Use

150 parts by weight of a hydroxy urethane with OH number 190, made from 26.5% 1,6-hexanediol, 21.0% trimethylolpropane, 1.8% ε-caprolactam and 50.7% diisocyanatotoluene (2,4- and 2,6 -Isomers in a ratio of 8: 2) are dissolved at 130 ° C. under reflux in 475 parts by weight of a mixture of equal parts by weight of cresol and xylene and, after cooling, mixed with 375 parts by weight of the solution of the blocked polyisocyanate prepared as described under a). 3 parts by weight of an aldimine based on butyraldehyde and aniline (1% based on LC) were added as catalyst.

On a vertical wire coating machine with a 4 m long oven, a copper wire with a diameter of 0.7 mm is coated with a felt wiper in 6 passes to a diameter increase of 50 µm. At a furnace temperature of 350 ° C, painting can be carried out in a travel range of 10 - 20 m / min without cracking when the copper wire is stretched until the paint film breaks. The enamelled wire obtained has a remarkably good abrasion strength and can be tinned at 320 ° C. (When testing the abrasion resistance according to the NEMA method,> 100 double strokes can be endured with a bearing weight of 400 p.)

When using the conventional hardener mentioned in Example 1 by equivalent exchange of the polyisocyanate according to the invention, the enamelled wire obtained under otherwise analogous coating conditions cannot be tinned at 320 ° C., or the tinning time is significantly above 10 seconds depending on the degree of baking. The abrasion resistance is significantly poorer; only about half of the double strokes are sustained, as described above.

Example 3 a) Manufacturing

2,589 parts by weight of cresol (technical isomer mixture) are allowed to flow in rapidly at 80 ° C., starting with heating up to 130 ° C., to 2,979 parts by weight of diisocyanatotoluene (2,4- and 2,6-isomers in a weight ratio of 8: 2). After about 12 hours, an isocyanate content of 7.5% is reached, and 1-methoxypropyl-2-acetate is dissolved by adding 3,000 parts by weight. A suspension of 432 parts by weight of melamine in a further 1,000 parts by weight of 1-methoxypropyl-2-acetate is allowed to flow in below 80 ° C. After heating to 140 ° C., the suspension becomes clear after about 2.5 hours in the course of the reaction, and the reaction is ended after about 1 hour of stirring time when the NCO content has dropped to zero.

A clearly resolved product is obtained with the following characteristics: Concentration: 60% Viscosity _η (23 ° C): 20,000 mPas free NCO content: <0.1% blocked NCO content (found): 9.9% blocked NCO content (calc.): 10.1% 1,3,5-triazine units (calc.): 2.7% Urethane groups (calc.): 0%

b) Use

150 parts by weight of the hydroxyurethane described in Example 2b) are dissolved in 600 parts by weight of a mixture of equal parts by weight of cresol and xylene under reflux at temperatures up to 130 ° C. The solution obtained is mixed with 250 parts by weight of the solution of the blocked isocyanate prepared as described under a) above. Then 3 parts by weight of an aldimine based on butyraldehyde / aniline as a catalyst (1%, based on LC) are added to the coating mixture thus obtained.

On a wire coating machine with a stoving shaft of 4 m length, a copper wire of 0.7 mm diameter is coated in 6 passes with a wiper felt to a diameter increase of 50 µm. At a temperature of the stoving shaft of 400 ° C, the speed of the wire can be varied from 8 m / min to 20 m / min. A perfectly painted wire is obtained within this burn-in area.

When testing for water breakage (hairline cracks), the enamelled wire behaves satisfactorily; it can be bent under water around a 20 mm diameter mandrel without hairline cracks. For testing, the wire is bent in a 0.5% NaCl solution around a narrowing mandrel starting at 100 mm in diameter and a direct voltage of 100 V is applied to the water bath and the copper conductor; no current flow is observed.

Example 4 a) Manufacturing

3,085 parts by weight of diisocyanatotoluene (2,4- and 2,6-isomers in a weight ratio of 8: 2) are blocked with 2,298 parts by weight of cresol (technical-grade isomer mixture) as described in Example 1a). After an NCO content of 11.1% (NCO _theor = 11.1%) has been reached, 4,000 parts by weight of 1-methoxypropyl-2-acetate are added as solvent. A mixture of 298 parts by weight of melamine and 319 parts by weight of 1,3-butanediol is added to the clear solution which has cooled to 60 ° C., and the mixture is left to react at 80 ° C. for 2 hours. The reaction mixture, which is still heterogeneous, is then heated to 140 ° C., and the reaction is terminated at this temperature until a clear solution is reached. Concentration: 60% Viscosity _η (23 ° C): 8,800 mPas free NCO content: 0.2% blocked NCO content (calc.): 8.9% 1,3,5-triazine units (calc.): 1.8% Urethane groups (calc.): 4.2%

b) Use

150 parts by weight of the hydroxyl urethane having the OH number 190 as described in Example 2b) are dissolved with heating in 600 parts by weight of a mixture of equal parts by weight of N-methylpyrrolidone and 1-methoxypropyl-2-acetate. The solution obtained is mixed with 250 parts by weight of the solution prepared as described under a) above, and 3 parts by weight of an aldimine based on butyraldehyde / aniline are added as a catalyst.

On a wire coating machine with a 4 m long stoving shaft at an oven temperature of 400 ° C, a copper wire with a diameter of 0.7 mm is coated in 6 passes with a wiper felt to a diameter increase of 50 µm.

The enamelled wire produced in this way has excellent adhesive strength. In the test according to DIN 46 453 8.4, the number of twists of more than 500 is achieved before the first paint layer detachments occur.

For comparison, a wire is lacquered under the same conditions as described above, but the blocked polyisocyanate according to the invention from Example 4a) was replaced by an equivalent amount of the conventional, commercially available product described in Example 1b). With the adhesive strength test according to DIN 46 453 8.4, only twist numbers up to approx. 350 can be achieved. The adhesive strength of the paint according to the invention is much better.

Example 5 a) Manufacturing

A diisocyanate mixture of 1,197 parts by weight of diisocyanatotoluene (2,4- and 2,6-isomers in a weight ratio of 8: 2) and 1,719 parts by weight of 4,4'-diisocyanatodiphenylmethane is started at 80 ° C with heating to 130 ° C with 1,486 parts by weight of cresol (technical Isomer mixture) added. After approximately 8 hours at 130 ° C. and an NCO content of 13.1% (NCO _theor. = 13.1%), 5,000 parts by weight of 1-methoxypropyl-2-acetate are added, and the _mixture is mixed at 60 ° C. a mixture of 289 parts by weight of melamine and 309 parts by weight of 1,3-butanediol. The mixture is left to react at 80 ° C. for 2 hours and at 140 ° C. for 2 hours until a clear solution is obtained.

The clear light yellow solution has the following characteristics: Concentration: 50% Viscosity _η (23 ° C): 17,500 mPas free NCO content: <0.1% blocked NCO content (calc.): 5.8% 1,3,5-triazine units (calc.): 1.8% Urethane groups (calc.): 4.1%

b) Use

150 parts by weight of the hydroxyurethane described in Example 2b) are dissolved in 550 parts by weight of a mixture of equal parts by weight of N-methylpyrrolidone and 1-methoxypropyl-2-acetate with heating to 130 ° C. 300 parts by weight of the blocked polyisocyanate solution prepared as described under a) above and 3 parts by weight of a catalyst, an aldimine based on butyraldehyde / aniline, are added to the cooled solution.

On a wire coating machine with a 4 m long stoving shaft, a copper wire with a diameter of 0.7 mm is coated in 6 passes with a scraper felt at an oven temperature of 400 ° C to a diameter increase of 50 µm.

A magnet wire with excellent hairline resistance is obtained. After the mandrel bending test described in example 3b), the enamelled wire can be bent around a mandrel of 20 mm without hairline cracks occurring.

Example 6 a) Manufacturing

To a mixture of 2046 parts by weight of 1-methoxy-2-propanol, 339 parts by weight of trimethylolpropane and 318 parts by weight of melamine heated to 80 ° C., 3,297 parts by weight of diisocyanatotoluene (2,4- and 2,6-isomers in a weight ratio of 8: 2) added dropwise so that the temperature is kept below 100 ° C. during an exothermic reaction. The reaction mixture, which becomes more viscous, is heated to 110 ° C. after approximately 1 hour and to 140 ° C. after approximately 1.5 hours. After about 2.5 hours no free isocyanate is detectable and 4,000 parts by weight of 1-methoxy-2-propanol are added as solvent. A clear, colorless solution of the polyisocyanate blocked with methoxypropanol is obtained with the following characteristics: Concentration: 60% Viscosity _η (23 ° C): 2,800 mPas free NCO content: NCO free blocked NCO content (calc.): 9.5% 1,3,5-triazine units (calc.): 2.0% Urethane groups (calc.): 4.5%

b) Use

150 parts by weight of the hydroxyurethane described in Example 2b) are heated in 600 parts by weight of a solvent mixture of equal parts by weight of N-methylpyrrolidone and 1-methoxypropyl-2-acetate dissolved at 130 ° C. The cooled solution is mixed with 250 parts by weight of the solution of the blocked polyisocyanate prepared as described under a) and mixed with 3 parts by weight of zinc octoate (Zn content = 8%) as a catalyst (1% based on LC).

On a vertical wire coating machine with felt wipers, a copper wire with a diameter of 0.7 mm is coated in 6 passes with a diameter increase of approx. 50 µm. The furnace shaft temperature was 400 ° C. The wire coating speed was varied from 12 m / min to 16 m / min.

In the lacquered wire obtained, the heat shock resistance is up to a temperature of 260 ° C and thus shows excellent values.

The heat shock test is carried out in accordance with DIN 46 453 by winding the enamelled wire around a mandrel of its own diameter (0.7 mm), so that 10 adjacent turns are formed. Three such coils are stored for 30 minutes in a cabinet preheated to 260 ° C. The lacquer film of the previously perfect coil then shows no cracks or breaks.

Example 7 a) Manufacturing

In 2,000 parts by weight of 1-methoxypropyl-2-acetate, 1,782 parts by weight of butanone oxime and 215 parts by weight of Mela min and 384 parts by weight of 1,3-butanediol. A solution of 1,485 parts by weight of diisocyanatotoluene (2,4- and 2,6-isomers in a weight ratio of 8: 2) and 2,134 parts by weight of 4,4'-diisocyanatodiphenylmethane in 2,000 parts by weight of 1-methoxypropyl- 2-Acetate added dropwise. The initially exothermic reaction mixture is stirred for about 2 hours at 80 ° C. and then for 1 hour at 140 ° C. until no free isocyanate is present and a clear solution has formed.

The clear yellow colored solution has the following characteristics: Concentration: 60% Viscosity _η (23 ° C): 4,320 mPas free NCO content: NCO free blocked NCO content (calc.): 8.6% 1,3,5-triazine units (calc.): 1.3% Urethane groups (calc.): 5.0%

b) Use

150 parts by weight of the hydroxyurethane described in Example 2b) are dissolved in 600 parts by weight of a solvent mixture of the same parts by weight of N-methylpyrrolidone and 1-methoxypropyl-2-acetate with heating to 130 ° C. and after cooling with 250 parts by weight of those prepared as described under a) Solution of the blocked polyisocyanate added. 3 parts by weight of zinc octoate (Zn content = 8%) are added as a catalyst.

As described in Example 6b), a copper wire with a diameter of 0.7 mm is coated under the same stoving conditions. The wire coating speed is varied from 10 to 16 m / min.

The heat shock resistance (test as described in Example 6b) is given up to 260 ° C and thus also shows excellent values.

Example 8 use

230 parts by weight of the 65% solution in 1-methoxypropyl-2-acetate of a hydroxy urethane, made from 22.1% trimethylolpropane, 8.7% diethylene glycol, 7.4% 1,3-butanediol and 61.8% 4.4 ′ -Diisocyanatodiphenylmethane are mixed with 395 parts by weight of a mixture of equal parts by weight of cresol and xylene. 375 parts by weight of the solution of the blocked polyisocyanate prepared as described in Example 1a) are added, and 3 parts by weight of an aldimine from butyraldehyde / aniline are used as catalysts.

In the wire coating system described in the preceding examples, a copper wire of 0.7 mm in diameter is coated in 6 passes with a felt wiper to an increase in diameter of 50 μm at an oven temperature of 400 ° C. The painting speed could vary from 10 - 22 m / min. The enamelled wire obtained is characterized by a particularly high abrasion resistance. With a bearing weight of 380 p, it can withstand 120 double strokes (test as described in example 2b). In addition, the enamelled wire has a good softening temperature; the test temperature of 250 ° C is withstood (DIN 46 453 10.1).

Claims (8)

1. Lacquer polyisocyanates with blocked isocyanate groups, characterized by the simultaneous presence of (i) 0.5-15% by weight of structural units of the formula incorporated via urea groups

(ii) 5-20% by weight of isocyanate groups (calculated as -NCO) in a form blocked with blocking agents for isocyanate groups and (iii) 0-30% by weight of other chemically incorporated urethane groups of the formula which differ from the blocked isocyanate groups
-NH-CO-O-. 2. A process for the preparation of paint polyisocyanates with blocked isocyanate groups according to claim 1, characterized in that a) organic diisocyanates with a molecular weight of 160-300 b) blocking agents for isocyanate groups, c) amino groups-containing triazines of the formula

in which
R represents an amino group or a substituent which is inert towards isocyanate groups
and if necessary d) organic polyhydroxyl compounds in the molecular weight range 62-3,000
reacted, the amount of blocking agent b) being used in an amount sufficient to block 20-90% of the isocyanate groups of component a) and components c) and d) in an amount which is still present after the blocking reaction in an equivalent ratio free isocyanate groups to amino and Hydroxyl groups correspond to from 0.65: 1 to 1.05: 1, the equivalent ratio of amino groups of component c) to hydroxyl groups of component d) being 1: 0 to 1:20, and the reactants a) to d) in in any order. 3. The method according to claim 2, characterized in that the blocking agent b) is used in an amount sufficient to block 35-80% of the isocyanate groups of component a), and components c) and d) in such an amount used which corresponds to an equivalent ratio of unblocked isocyanate groups to amino and hydroxyl groups still present after the blocking reaction of 0.8: 1 to 1: 1, the equivalent ratio of amino groups of component c) to hydroxyl groups of component d) at 1: 0 to 1: 4 lies. 4. The method according to claim 2 and 3, characterized in that blocking agent selected from the group consisting of phenols, aliphatic alcohols, oximes and lactams is used as component b). 5. The method according to claim 2 to 4, characterized in that melamine is used as component c). 6. The method according to claim 2 to 5, characterized in that one uses as component d) optionally having ether bridges or built-in isocyanurate rings having (cyclo) aliphatic, polyhydric alcohols of the molecular weight range 62-350. 7. Use of the lacquer polyisocyanates according to claim 1 in combination with organic polyhydroxyl compounds as stoving lacquer or for producing a stoving lacquer for any heat-resistant substrates. 8. Use according to claim 7 as a stoving lacquer for wire coating or for producing a stoving lacquer for wire coating.